Is the Veeam files to tape layout compatible with any third party tools? Specifically, I am thinking of CPIO, tar, or any other similar utilities? I need to dump the contents of several tapes and was unaware, until we had a problem, that Veeam was entirely unhelpful in this scenario.

As different vendors leverage different MFT specification, they cannot browse tapes written by each other. Speaking of dumping content of tapes, what kind of tape job do you use? Backup to tape one or file to tape one? Do you have Veeam ONE deployed?